Solar thermal installations built around a central tower have long been limited to mere tech demonstrations and R&D facilities, until now. In conjunction with Nord Drivesystems, Gemasolar, in the south of France, is now making the leap to full-scale production sites. In order to ensure precise and reliable operation of the plant's mobile heliostats that focus the sunlight, the vast array comprising of 2,650 mirrors is equipped with 5,300 robust gearmotors supplied by Nord Drivesystems.
The Gemasolar plant's basic set-up consists of a central tower with a receptor area at the top of the structure, a liquid circulation cycle including storage tanks and heat exchanger facilities for power generation via an adjacent turbine, and an array of mirror units that focus the rays of the sun onto the receiver. These mirrors are designed to turn and tilt, following the sun, in order to ensure that as much sunlight as possible is reflected onto the designated area on the tower from dawn till dusk. Nord Drivesystems has supplied 5,300 gearmotors from their Nordbloc.1 product line for the Gemasolar heliostats. In each of the 2,650 flat mirror units, two Nordbloc.1 gearmotors enable highly accurate movements for two axes to track the path of the sun.
The Gemasolar site extends over an area of 460 acres to accommodate the vast field of heliostats. Operated by Torresol, a joint venture between Spanish engineering giant Sener Ingeniería y Sistemas and Masdar, Abu Dhabi's state-owned future energy enterprise, Gemasolar is the first ever commercial-scale CSP (concentrated solar power) plant with central tower technology that implements a heat storage system based on molten salts. Liquefied nitrate salts are pumped up from a storage tank, run through the receiver section, and absorb the heat impact of the highly concentrated solar radiation in that tower segment made possible by 5,300 Nord Drivesystems Nordbloc.1 series gearmotors. The temperature of the liquid that has passed through it usually exceeds 930 degrees F. Once they leave the receptor, the molten salts flow through a heat exchanger where they cool down again, with the resulting water vapor driving a steam turbine that feeds a generator. The generated energy is supplied into the electrical grid. Most notably, though, the molten salts cycle at Gemasolar incorporates an innovative storage option. Whenever there is more heat energy available than the turbine is able to convert, the extra energy is stored by diverting some of the flow of molten salts before the liquid reaches the heat exchanger. Kept in a special tank, the hot medium can be used at a later time when insufficient solar radiation - or none at all - is available for standard operation of the plant. This solution enables the system to generate power from stored heat for up to 15 hours, i.e. throughout long periods of cloudy skies or even darkness. The resulting total of 6,500 hours of productive operation per year makes this plant much more efficient than more conventional renewable energy facilities that are totally dependent on changing conditions.
The sunlight concentration is achieved by 2,650 flat mirrors all continually pointing at the same receiver region on the installation´s one central tower. Given the size, weight, and shape of these mirror units, each of them depends on a powerful, sturdy, and robust drive solution to ensure reliable tracking of the sun. Obviously, this is an application exposed to very rugged environmental conditions, so all equipment used here must be manufactured to withstand extreme application factors. Moreover, each heliostat has a flat surface of about 400 ft², which makes them markedly susceptible to strong, not to mention gale-force winds that naturally occur from time to time. Still, proper operation of the heliostats and the power plant as a whole is ensured in all but the most extreme weather conditions. The Nordbloc.1 geamotors working throughout the array of mirrors play an instrumental part in that. Torresol's heliostats are equipped with robust case size 5 Nordbloc.1 series geared motors. Compared to same size previous generations of the Nordbloc housing solutions, these gearmotors are suitable for much greater forces than before. Mounting options are particularly user-friendly, allowing for cost-efficient, direct motor mounting, or an attachment of very short, space-saving lightweight motor adapters. These many product options were pivotal in the ease of the Nordbloc.1 gearmotor integration into the design of Torresol's heliostats. The gearmotors aluminum alloy housings provide robust, natural corrosion protection out of the box - without the need for a paint finish.
Through the use of Finite Element Analysis (FEA) Nord Drivesystems optimized the Nordbloc.1 series design, these models are not only considerably lighter than their predecessors, but also one of the most reliable and durable gearboxes on the market. For gearmotors up to case size 6, the Unicase design enables the mounting of larger bearings. The units therefore withstand higher overhung loads or last longer under a given load.